When Ashaya dies, Nim Deathmantle triggers, causing you to pay ({4} magic symbol) to return Ashaya from your graveyard to the battlefield, and attaching Nim Deathmantle to it.
When Ashaya enters the battlefield, each Scute Swarm you control triggers, creating that many 1/1 Insect creature tokens or token copies of Scute Swarm.
Activate Ashnod's Altar by sacrificing a creature token, adding ({C} magic symbol) ({C} magic symbol) .
Repeat.
If you control a nontoken creature that has haste, you may instead sacrifice it, and then tap it each iteration to get infinite green mana and colorless mana.